Means for loading operating spring of a circuit breaker

ABSTRACT

A spring powered over-center toggle circuit breaker contact operating mechanism is constructed with a generally U-shaped operating member pivotally mounted to the mechanism frame on stud means extending outward from each side of the frame. Each arm of the operating member at the free end thereof is provided with two arcuate notches which selectively receive the stud means. When the stud means is received by one of the arcuate notches, the operating member is so positioned that the main operating spring is relaxed to facilitate assembly of the mechanism elements. After this assembly is completed, the operating member is repositioned by having the stud means received by the other of the arcuate notches. This repositioning stretches the main operating spring for loading thereof to apply full contact operating forces.

MEANS FOR LOADING OPERATING SPRING OF A CIRCUIT BREAKER [75] Inventor: Albert Strobel, Cherry Hill, NJ.

[73] Assignee: I-T-E Imperial Corporation,

Philadelphia, Pa.

[22]- Filed: July 27, 1972 [21] Appl. No.: 275,569

[52] US. Cl 200/153 G, 335/191, 337/59, 337/132 [51] Int. Cl. H0lh 3/46 [58] Field of Search 200/153 G, 153 H, 83 S, '200/67 B; 335/191; 337/59, 132

[56] References Cited UNITED STATES PATENTS 3,235,689 2/1966 Poulton, Jr. 337/59 X 3,182,149 5/1965 Noakes 200/83 S X 1,786,796 12/1930 Von Hoom 337/59 Apr. 30, 1974 tending outward from each side of the frame. Each arm of the operating member at the free end thereof is provided with two arcuate notches which selectively receive the stud means. When the stud means is received by one of the arcuate notches, the operating member is so positioned that the main operating spring is relaxed to facilitate assembly of the mechanism elements. After this assembly is completed, the operating member is repositioned by having the stud means received by the other of the arcuate notches. This repositioning stretches the main operating spring for loading thereof to apply full contact operating forces.

.4 C aim 10 a n i u e PATENTEDAPR 30 m4 SHEET 1 BF 6 sleoalaee PATENTEI] APR 3 0 i974 SHEET 2 OF 6 MEANS FOR LOADING OPERATING SPRING OF A CIRCUIT BREAKER This invention isrelated to molded case ciruit breakers in general, and more particularlyrelates to a spring powered over-center toggle contact operating mechanism therefor having anovel construction which facilitates assembly thereof.

As the current ratings of molded case circuit breakers have increased and the constructions thereof have remained very compact, assembly of the contact operating mechanism has become troublesome particularly because of the large size springs required to obtain high operating forces combined with space limitations making it difficult to manipulate the mechanism elements.

- thereafter the springs are loaded by repositioning the operatingmember extension of the handle with respect to the mechanism frame.

With the operating springs relaxed, the operating member is pivotally supported directly by bearing pins on the frame, and when the springs are loaded, the operating member is supported by bushing mounted on the bearing pins. This type of construction has two basic disadvantages in. that, as will be seen hereinafter, 7

four extra parts .(two bushings andv retainers therefor) are required for each mechanism assembly, and the bearing pins must be excessively long to mount the retainers and thereby occupy valuable space which is at a premium in compactly designed molded case circuit breakers. j

The aforesaid disadvantages are overcome by the instant invention which constructs the mechanism operating member with two sets of arcuate bearing notches that are selectively used to pivotally support the operating member directly on studsextending from opposite sides of the mechanism frame. These bearing notches are so positioned that the operating springs are either relaxed or fully loaded for contact operation depending upon which of these bearing notches receive the bearing studs on the frame. This eliminates the bushings and bushing retainers required by the prior art, and the frame mounted studs of the instant invention are much shorter than those of the prior art as exemplified by the teachings of the aforesaid U.S. Pat. No. 3,235,689.

Accordingly, a primary object of the instant invention is to provide a novel construction for a circuit breaker operating mechanism that is assembled with the main operating spring in a relaxed state.

Another object is to provide an operatingmechanism of this type that requires fewer elements than prior art mechanisms of this type.

Still another object is to provide an operating mechanism of this type that is more compact than prior art mechanisms of this type.

These objects as well as other objects of this inven tion will become readily apparent after reading the following description of the accompanying drawings in which:

FIG. 1 is a plan view of a circuit breaker constructed in accordance with teachings of the instant invention.

FIG. 2 is a longitudinal cross-section taken through line 2-2 of FIG. 1, looking in the direction of arrows 2'2 and including a handle operating mechanism, not shown in FIG. 1.

FIG. 3'is an exploded perspective of one overcenter toggle mechanism and selected elements connected thereto.

FIG. 4 is an exploded perspective of the movable contact structure for one pole.

FIG. 5 is a side elevation of the spring supporting opcrating member of the contact operating mechanism.

FIGS. 6 and 7 are plan and side elevations respectively of the operating member of FIG. 5, looking in the directions of the respective arrows 66 and 7-7 of FIG. 5.

FIG. 8 is a side elevation of the contact operating a mechanism for one pole with the near side of the frame removed.

FIG. 9-is an end view of one side of the mechanism frame showing mounting of a positive ON indicator lever and the position of the latter relative'to elements of the mechanism that cooperate with this lever.

FIG. 10 is an enlarged fragmentary longitudinal cross-section of the handle showing its mounting to the operating member of the center pole.

Now referring to the figures. Three phase molded case circuit breaker 25 of FIGS. 1 and 2 includes an individual over-center spring-powered toggle operating mechanism. Prior art examples of circuit breakers having more than a single operating mechanism for all pha' ses are disclosed in U.S. Pat. Nos. 2,067,935 and 3,125,653.

Circuit breaker 25 includes a molded housing constructed of base 26 and removable cover 27 joined along line 28 and provided with longitudinal internal partitions 31, 32 which divide housing 26, 27 into three longitudinally extending compartments, one for each phase of circuit breaker 25. Cover 27 is provided with aperture 29 through which stubby bifurcated extension 33 of operating handle means 30 extends. Each section of handle extension 33 receives an individual pin 34 extending upwardly from the web portion of inverted generally U-shaped operating yoke member 35 of the center phase. Operating members 35 of the outer phases are each secured to handle means 30 by a pair of screws 152.

Member 35 is pivoted to the spaced arms of generally U-shaped operating mechanism frame 36 at outwardly extending lugs 37. Bolts 48, received by threaded apertures of inturned edges 36a at the bottom of frame 36, fixedly secure the latter to base 26. Transverse tie member 49 is riveted to the arms of frame 36 to maintain spacing therebetween and to stabilize the frame structure.

Four-tensioned coil springs 38, each connected at oneend thereof to the web of operating member 35, combine to constitute the'main operating spring means for the overcenter toggle-type contact operating mechanism. The other ends of springs 38 are connected to spaced plates 39, 39 that are pivotally mounted to toggle knee pin 41 connecting upper 42 and lower 43 toggle links. The upper ends of upper toggle links 42 are pivotally connected to the spaced arms of latchable cradle 40 at pins 44, and the lower ends of lower toggle links 43 are pivotally connected to contact carrier 45 by rod 46 that extends between the spaced arms of contact carrier 45. The spaced arms of cradle 40 are positioned adjacent the inner surfaces of the spaced arms of frame 36 and are pivotally connected thereto by pins 47 that are secured to frame 36.

Under normal operating conditions plate 51, secured to web 40a of cradle 40, is in engagement with forward latching surface 52 of auxiliary latch 53. The latter is loosely mounted to pivot rod 55 extending between the spaced arm of mechanism frame 36 and slightly outboard thereof. The coiled end sections of torsion spring member 56 are wound about pivot rod 55, with the ends of these sections bearing against rod 57 and auxiliary latch 53 to bias the latter counterclockwise against stop rod 58. The ends of rods 57 and 58 are supported by the arms of frame 36. Leaf spring 73 secured to auxiliary latch 53 bears against pivot rod 55 biasing latch 53, so that rod 55 will normally lie at the central portion of V-shaped notch 74 of primary latch 53.

The ends of rod 55 projecting outboard of mechanism frame 36 are engaged by the hooked portions at the forward extension 59'of the arms for U-shaped trip unit frame 60, whose web portion is seated on a forward surface of load strap 61, being secured thereto by bolts 62 that extend through clearance apertures in strap 61 and are received by threaded inserts molded in base 26.

Rear latch tip 54 engages latch tip 63 at the U-shaped forward arm of primary latch 65, whose rear latch tip 64 is engaged by latch plate 67 mounted on one leg of L-shaped carrier 66. Primary latch 65 is pivotally mounted to trip unit frame 60 at stub shaft 69, and the carrier is pivoted on rod 68 to frame 60. Tension spring 75 biases primary latch 65 in a clockwise direction about pivot 69. The other leg of carrier 66 is provided with transversely extending pin 71 that projects into triangular window 72 of primary latch 65 at a portion thereof near rear latch tip 64, for a reason to be hereinafter explained. Tension spring 76, connected between frame 60 and carrier extension 66a, biases carrier 66 in a counterclockwise direction about its pivot 68 toward latching position.

When automatic tripping occurs, carrier 66 in the faulted phase is moved clockwise either by the deflection of bimetal 77 or movement of magnetic armature 78, causing latch plate 67 to release primary latch 65, which in turn releases secondary latch 53 and permits main operating springs 38 to rotate cradle 40 in a counterclockwise direction to break toggle 42, 43. The force from main spring 38 acts through cradle 40, primary latch 53, and secondary latch 65 to drive cam surface 78, bounding opening 72, against extension 71 to rotate carrier 66 clockwise, with surface 79 thereof engaging ear 8] of extension 82 on tripper bar 80 which extends between all three phases. This causes tripper bar 80 to rotate in a counterclockwise direction, so that extensions 82 in the non-faulted phases rotate counterclockwise with cam surfaces 83 thereof engaging transversely extending pin 84 of carriers 66 in the nonfaulted phases, rotating them clockwise or in the tripping direction, to release the cradle latching systems in the non-faulted phases, so that the contacts of all three phases are open.

In order to prevent closing of the contacts of any one phase before the operating mechanisms of all phases are latched, circuit breaker 25 is provided with a defeater latching system including defeater latch and defeater lever 90. Latch 80' is pivotally mounted upon rod 55 and includes protrusion 81' extending over the rear of cradle 40 when the latter is in latched position. Latch 80' further includes protrusion 82' extending over the forward end of defeater lever in slot 91 thereof. Coiled tension spring 83' is connected between stop rod 57 and latch 80, passing partially around rod 55, to bias latch 80' in a counterclockwise direction about its pivot 55 and maintaining this pivot in the basic position at the right end of slot 84' in latch 80. This basic position is established through the engagement of latch stop surface 86 and stop rod 57.

Slot 91 is in the web of the U-shaped forward portion of latch lever 90, with the U arms having pivot pin 69 for lever 90 extending therethrough. Rear portion 89 of lever 90 is positioned below and in interfering relationship with transverse pin 71 mounted to latch plate carrier 66. i

During normal relatching of circuit breaker 25, inwardly protruding portions of the operating member 35 arms engage outboard portions of pin 44 to pivot cradle 40 clockwise, whereby the latter cams defeater latch 80 away and moves below auxiliary latch 53. Upon release of the circuit breaker operating handle 30, the elements of the latch train 53, 65, 66 move into place. However, should any of these elements fail to properly engage or should cradle 40 not have been moved far enough to engage auxiliary latch 53, cradle 40 will pick up defeater latch protrusion 81', causing clockwise rotation of defeater latch 80'. In turn, this causes defeater latch protrusion 82' to engage defeater lever 90 and rotate the latter counterclockwise, with the rear end 89 thereof contacting carrier extension 71 so that latch plate carrier 66 is pivoted in a clockwise or latch train releasing direction. During this releasing movement of carrier 66, surface 79 thereof engages nose 81 of one trip bar extension 82 to rotate common tripper bar 80 in a counterclockwise direction, with the other extensions 82 on bar 80 engaging pins 84 on, the latch plate carriers 66 of the other poles, thereby causing the latch systems of all other poles to be released.

The lower end of bimetal 77 is fixedly secured to shading coil 99, and these elements are fixedly secured to molded frame member secured to trip unit frame 60. The horizontal leg of inverted U-shaped stationary magnetic frame member 98 passes through the center of coil 99. Member 98 is secured to the rear of frame 60, with the vertical legs of member 98 being on opposite sides of load strap 61. The other U-shaped magnetic frame member 96 is secured directly to load strap 61, with the ends of the arms for frame members 96 and 98 confronting one another in spaced relationship. Thus, current flowing in load strap 61 generates flux in magnetic frame 96, 98 which induces current flow in shading coil 99 and thereby generates heat that is conducted to bimetal 77 for heating thereof. Coiled tension spring 97, connected between armature 78 and an element mounted to the rear transverse part 60a of frame 60, biases the former away from two spaced legs 98a extending upward from the horizontal leg of member 98, and is drawn downward toward legs 98a when overload currents generate sufficient magnetic flux in magnetic frame 78, 96, 98.

With particular reference to FIG. 4, it is seen that the movable contact structure for each phase of circuit breaker 25 includes eight main contacts 103-410 and a single arcing contact 101. The latter contact 101 is mounted at the forward end of arm 112, which is pivotally mounted to carrier 45 at toggle connecting rod 46. Main contacts 103-110 are arranged in two parallel rows positioned to the rear of arcingcontact 101 and disposed at right angles to the plane of movement of arcing contact arm 112.

Main contacts 103-106 in the forward row are mounted to individual contact arms 113-116 respectively, all pivotally mounted to carrier 45 on rod 46. Main contacts 107-110 in the rear row are mounted to the forward end of the respective contact arms 117-120, respectively, pivotally mounted to carrier 45 on rod 102. All of the contact arms 112-120 are connected to load strap 61 by means of individual stacks 121 of flexible sheet conductors. Contact a'rms 113-116 are in alignment with and extend over the respective contact arms 117-120, so that the latter group of arms 117-120 block downward movement of the former group ofarms 113-116 to establish the open circuit position of contacts 103-106 in a manner which will hereinafter be seen. The open circuit position for arcing contact arm 112 is established through engagement thereof with aligned pins 123, 124 which mount the respective pairs of main contacts 117, 118 and 119, 120 to auxiliary carriers 125, 126 respectively. Notch 122 along the lower edge of arcing contact arm 112 provides clearance for pins 123, 124.

Auxiliary carrier 125 is an inverted U-shaped member whose arms extend downwardly through cutouts 131, 132 in the web portion of contact carrier 45 and straddle four contact arms 113, 114, 117, 118. Pin 123 secures contacts 117, 118 to the lower ends of the arms comprising auxiliary carrier 125. The web of auxiliary carrier 125 is biased towards the web of contact carrier 45 by coiled compression spring 127, which is wound around the threaded body of bolt 128 whose head is positioned below the web portions of contact carrier 45. Self-locking nut 133 mounted to bolt 128 is rotated to adjust the loading of spring 127, with the rectangular shoulder of bolt 128 cooperating with rectangular cutout in carrier 45 to prevent rotation of bolt 128. Thus, in the open circuit position, spring 127 biases the web of auxiliary contact carrier 125 against the web of contact carrier 45, and when the contacts are closed there is a space between the webs of these contact carriers 45, 125, so that the force exerted by spring 127 acts to bias contacts 107, 108 into firm electrical engagement with their respective cooperating contact portions on line strap 136.

The mounting of contact arms 119,120 to auxiliary contact carrier 126 and mounting of the latter to contact carrier 45 is the same as the mounting of contact arms 1 17, 1 18 and auxiliary carrier 125, so that this description will not be repeated.

Biasing forces for each of the contacts 103-106 in the forward row are provided by individual coiled compression springs 138, and each of these springs is mounted in the same way so that only the mounting of one of these springs will be described. The lower end of spring 138 extends into depression 139 in the upper surface of main contact arm 113, and the rear of spring 138 extends into tubular support 141 through the open bottom thereof. Support 141 is mounted to the upper surface of carrier 45 at the web portion thereof, and its upper end is threaded to receive adjusting screw 142 whose lower end bears against disc 143 abutting the upper end of spring 138. If screw 142 is adjusted to set the contact pressure exerted by spring 138, lock nut 144 is tightened to lock this adjustment.

In order to increase the area of engagement between main contacts 103-110 and their respective cooperating stationary main contacts in the very limited space available, it is noted that each of the main contacts is provided with a portion extending outward of its respective contact arm. That is, in order to utilize the space below arcing contact 112, main contacts 104, 105, 108, 109 havebeen extended beyond their respective contact arms 114, 115, 118, 119 to project below arcing contact arm 112. Similarly, main contacts 103, 106, 107, have been extended outboard from their respective contact arms 113, 116, 117, 120, to lie in the space below the outboard arms of auxiliary contact carrier 125, 126 and other elements used to connect the movable contact structure to the contact operating mechanism.

The forward end of arcing contact arm 112 is biased downward away from the web portion of contact carrier45 by coiled compression spring 171 whose lo wer end is positioned by pin 172 extending upward from arm 112. The upper end of spring 171 extends into tubular member 173, on the upper surface of the carrier 45 web portion, through the bottom of member 173 and abuts the closed upper end thereof.

The spaced arms of contact carrier 45 are provided with rearward extensions 45a, 45b that are spaced by and secured to shouldered cylindrical tube 146. After all contact structures, operating mechanisms, latching devices, and automatic trip units are mounted to base 26, and all adjustments to these mechanisms have been made, the contact structures of all phases are'operated to the closed position, so that the tubular members 146 of all phases are axially aligned and are positioned above barriers 31, 32 and the longitudinal sides of base 26. Thereafter, cylindrical tie bar 147 is driven longitudinally in the members 146 of all phases to constitute a rigid mechanical connection between the movable contact structures of all phases. The fit between tie rod 147 and tubular members 146 is tight enough to prevent unintentional axial movement of tie rod 147, yet permits tie rod 147 to be removed for convenient servicing and replacement of parts.'Mechanism frame 36 is provided with aligned elongated slots 148 to provide clearances for movement of rod 147 during opening and closing of the movable contact structures.

The construction of operating member 35 is best seen by reference to FIGS. 5-7. In particular, inverted U-shaped operating member 35 includes spaced arms 201, 202 connected at their upper ends by web 203. Each arm is provided with an inwardly extending cradle engaging resetting protrusion 204, and an elongated slot 205 which receives outwardly extending pin 21 l at the upper end of an individual S-shaped lever 210 which, as will hereinafter be described, functions as the key element of a positive ON indicating means. Web 203 is provided with four pairs of apertures 213, 214 through which the upper ends of springs 38 are hooked. Threaded apertures 215 in web 203 receive the threaded ends of shoulder pins 34 (FIG. 10) in the case of the center pole mechanism, and for the outer poles threaded apertures 215 receive fastening bolts 152.

The lower or free end of each arm 201, 202 is provided with a pair of arcuate bearing notches 238, 239. During assembly of the contact operating mechanism,

frame supported bearing studs 37 are received by bearing notches 238, and in this position of operating member 35'springs 38 are substantially relaxed, thereby permitting the mechanism elements to be moved readily to positions where they may be assembled conveniently.-

After the mechanism elements are assembled, operating member 35 is moved to a new position wherein bearing studs 37 are received by arcuate notches 239. This repositioning of operating member 35 fully loads springs 38 for contact operation and contact pressure. This increase in spring pressure results from thefact that the distance between web 203, and operating bearing notch 239 is greater than the distance between assembly bearing notch 238 and spring supporting web 203, so that the repositioning of operating member 35 moves the upper ends of main spring sections 38 away from the lower ends thereof which are secured to members 39 pivotally mounted on toggle knee. Each S- shaped lever 210 is pivotally mounted to a pin 209 extending outward from the side of mechanism frame 36 (See FIGS. 8 and 9). At a point between pivot 209 and pin 211, lever' 210 is provided with pin means 212 extending inwardly through a clearance aperture 191 in frame 36 to cooperate with lower toggle link 43 and prevent operating member 35, and handle 30 secured thereto, from moving to a contact open position unless the contacts are actually open.

More particularly, when handle 30 is moved in a clockwise direction with respect to FIG. 8 to open circuit breaker 25, acting through pin 211 in slot 205, operating member 35 moves lever 210 clockwise about pivot 209. This moves pin 212 on lever 210 toward knee 41 of toggle 42, 43. However, unless toggle 42, 43 collapses, and this may only occur when contact carrier 45 moves to open circuit position, lower toggle link 43 blocks movement of pin 212 so that pin 211 prevents handle 30 from pivoting clockwise to open circuit position. In the event there is a minor malfunction of the contact operating mechanism causing carrier 45 to stick in contact closed position, the engagement of pin 212 with link 43 may collapse toggle 42, 43 to bring about contact opening.

The constructions and functions of insulating disks 235, 236 (FIG. 10) mounted on movable contact tie bar 147, and barrier sheets 231, 232 mounted to handle 30 by. screws 230 are described in one or more of the copending applications referred to in the following paragraph of this application. Similarly, the constructions and functions of roller 222 and washers 223 are all mounted to handle extension 33 by roll pin 233 are described in one or more of the aforesaid copending applications.

For those features of construction in circuit breaker 25 that have not been described herein, reference is made to one or more of the copending applications Ser. Nos. 275,568, 275,577, 275,446, 275,578, 275,507, 275,454, 275,508, 275,621, 275,623, 275,624, 275,522, 275,521, 275,523, and 275,622, all filed of even date herewith, and all assigned to the assignee of the instant invention.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now become apparent to those skilled in the art. Therefore, this invention is to be limited not by the specific disclosure herein but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A circuit breaker operating mechanism including support means; an operating member; contact means operatively connected between said support means and said operating member; cooperating first and second means, one on said operating member and the other on said support means, pivotally mounting said operating member to said support means; said second means including spaced first and second bearing sections constituted by integrally formed portions of a common member, and said first means comprising a third bearing section selectively engageable with said first and said second sections to pivotally mount said operating member; said sections being operatively positioned so thatwith said first and third sections operatively engaged said spring means is loaded for normal operation of said contact means, and with said second and third sections operatively engaged said spring means is substantially relaxed to facilitate assembly of said mechanism; said operating mechanism comprising a generally U-shaped member including a web portion to which one end of said spring means is connected, and generally parallel arms extending from said web portion; said first section comprising aligned arcuate notches in the free ends of said arms and said second section comprising aligned arcuate notches in said free ends; said third section comprising pin means on said support.

2. A circuit breaker operating mechanism as set forth in claim 1 also including a latchable cradle pivotally mounted on said support means and toggle link means connected at opposite ends thereof to said cradle and said contact means, respectively; said toggle means having a knee to which said spring means is connected.

3. A circuit breaker as set forth in claim 2 in which the support means comprises a frame having spaced sides; said third means comprising stud means extending outboard from each of said sides of said frame.

4. A circuit breaker operating mechanism including support means; an operating member; contact means operatively connected between said support means and said operating member; cooperating first and second means, one on said operating member and the other on said support means, pivotally mounting said operating member to said support means; said second means including spaced first and second bearing sections, and said first means comprising a third bearing section selectively engageable with said first and said second sections to pivotally mount said operating member; said sections being operatively positioned so that with said first and third sections operatively engaged said spring means is loaded for normal operation of said contact means, and with said second and third sections operatively engaged said spring means is substantially relaxed to facilitate assembly of said mechanism; said operating member including an arm having a free end where said second means is disposed; said first and second sections comprising respective first and second notches at said free end; and said third section comprising stationary bearing pin means on said support means. 

1. A circuit breaker operating mechanism including support means; an operating member; contact means operatively connected between said support means and said operating member; cooperating first and second means, one on said operating member and the other on said support means, pivotally mounting said operating member to said support means; said second means including spaced first and second bearing sections constituted by integrally formed portions of a common member, and said first means comprising a third bearing section selectively engageable with said first and said second sections to pivotally mount said operating member; said sections being operatively positioned so that with said first and third sections operatively engaged said spring means is loaded for normal operation of said contact means, and with said second and third sections operatively engaged said spring means is substantially relaxed to facilitate assembly of said mechanism; said operating mechanism comprising a generally U-shaped member including a web portion to which one end of said spring means is connected, and generally parallel arms extending from said web portion; said first section comprising aligned arcuate notches in the free ends of said arms and said second section comprising aligned arcuate notches in said free ends; said third section comprising pin means on said support.
 2. A circuit breaker operating mechanism as set forth in claim 1 also including a latchable cradle pivotally mounted on said support means and toggle link means connected at opposite ends thereof to said cradle and said contact means, respectively; said toggle means having a knee to which said spring means is connected.
 3. A circuit breaker as set forth in claim 2 in which the support means comprises a frame having spaced sides; said third means comprising stud means extending outboard from each of said sides of said frame.
 4. A circuit breaker operating mechanism including support means; an operating member; contact means operatively connected between said support means and said operating member; cooperating first and second means, one on said operating member and the other on said support means, pivotally mounting said operating member to said support means; said second means including spaced first and second bearing sections, and said first means comprising a third bearing section selectively engageable with said first and said second sections to pivotally mount said operating member; said sections being operatively positioned so that wIth said first and third sections operatively engaged said spring means is loaded for normal operation of said contact means, and with said second and third sections operatively engaged said spring means is substantially relaxed to facilitate assembly of said mechanism; said operating member including an arm having a free end where said second means is disposed; said first and second sections comprising respective first and second notches at said free end; and said third section comprising stationary bearing pin means on said support means. 